The present invention relates to a propeller having adjustable (or variable-pitch) feathering blades, particularly for use in sail boats.
Propellers of the above type have already been known in the art and in these propellers che feathering character of the blades is necessary in order to reduce as much as possible the resistance thereof to the boat moving forward when said boat is pushed by other propulsory means such as, in this case, the sails. In addition, the possibility of varying the blade orientation, that is the propeller pitch is an essential feature for optimizing the propeller efficiency, based on the mechanical characteristics of the propulsor used and the hydrodynamic characteristics of the boat.
Therefore in propellers of this type there is the presence of means enabling the blades to be automatically adjusted to the previously set correct positions for the two directions of rotation of the propulsor's drive shaft corresponding to the forward and reverse speed respectively.
These known propellers usually comprise a hub fixedly mounted to the end of the drive shaft and externally carrying a bevel pinion with which respective bevel pinions mesh, the axes of which are perpendicular to the hub axis and which are provided at the end of the propeller blades and surrounded by a multi-section shell covering the hub.
The hub can freely rotate within said shell making the blades rotate about their own axes in either direction through a given predetermined angle, and is subsequently brought into engagement with the outer shell driving it in rotation integrally therewith. The stroke stops disposed between the hub and the shell therefore define the orientation of the blades, that is the propeller pitch in the two directions of rotation of the drive shaft corresponding to the boat movements.
In some propellers of the above type the stroke stops disposed between the hub and the outer shell cannot be modified and consequently they do not enable the propeller to be adapted to different propulsors and/or boats.
In other known propellers it is possible to modify the angular positions of said stroke stops and, as a result, the propeller pitch, but in this case it is necessary to resort to the propeller dismantling and remounting, which needs the boat to be beached.
In addition, also available are variable-pitch propellers having feathering blades, in which the propeller pitch can be modified without resorting to the complete dismantling thereof and therefore without being obliged to beach the boat.
For example the Italian Patent Application No. 83647-A/87 filed on Aug. 11, 1987 describes a variable-pitch propeller having feathering blades, in which the propeller pitch can be modified by acting on the end of a rod issuing from the ogive-shaped end portion of the propeller and connected, at the other end thereof, to the hub fitted to the drive shaft.
Such an embodiment is rather complicated and a great number of components are required so that the adjustment of the propeller pitch may be carried out. In addition, in this embodiment the outer shell covering the hub consists of longitudinal sectors to be coupled and fixed by means of tangentially-disposed screws. Such a conformation of the shell in the long run can give rise to breaks or at least untightenings involving infiltrations that may be damaging for a good operation of the propeller.